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`1) x^2 - 4xy + 4y^2 - 9z^2`

` = (x^2-4xy+4y^2)  - 9z^2`

`= (x-2y)^2 - (3z)^2`

` = (x-2y-3z)(x-2y+3z)`

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`2) \sqrt{3 + 2 \sqrt{2}} - \sqrt{3  - 2 \sqrt{2}}`

` = \sqrt{2 + 2\sqrt{2} + 1} - \sqrt{2-2\sqrt{2}+1}`

` = \sqrt{ (\sqrt{2})^2 + 2.\sqrt{2} . 1 + 1^2} - \sqrt{ (\sqrt{2})^2 - 2.\sqrt{2}.1+1^2}`

` = \sqrt{ (\sqrt{2}+1)^2} - \sqrt{ (\sqrt{2}-1)^2}`

` = |\sqrt{2}+1| - |\sqrt{2} - 1|`

` = (\sqrt{2}+1)- (\sqrt{2}-1)`

` =\sqrt{2} + 1-\sqrt{2}+1`

` =2`

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`3) |3x+2|=7`

`<=>3x+2=7` hoặc `3x+2=-7`

`***)3x+2=7<=>3x=5<=>x=5/3`

`***)3x+2=-7<=>3x=-9<=>x=-3`

Vậy phương trình đã cho có tập nghiệm `S={5/3;-3}`